Golf ball inspection using metal markers

ABSTRACT

A method for inspecting a golf ball comprising the steps of providing a golf ball comprising a core and a cover; providing at least one flat reference marker; abutting the golf ball against at least one marker; rotating the golf ball about a single axis; capturing an x-ray image of the golf ball and marker; and determining the eccentricity of the golf ball.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a continuation of U.S. application Ser. No.10/229,614, filed Aug. 28, 2002 now U.S. Pat. No. 6,757,353.

FIELD OF THE INVENTION

This invention relates generally to golf ball inspection. Moreparticularly, this invention relates to golf ball inspection forconcentricity of internal components using x-rays.

BACKGROUND OF THE INVENTION

While the majority of golf balls today are solid, back in the thirties,golf balls were generally only of wound construction. The wound ball wascomprised of a center, windings, and a cover. One day, Philip E. Youngdecided to see if the wound golf ball center he was playing wasconcentric and asked his golfing partner, a dentist, to x-ray the ball.Sure enough, the x-ray showed that the center of his ball was notconcentric. As a result, Mr. Young founded the Acushnet Process Companyand began making golf balls that were all x-ray inspected forconcentricity.

Heretofore, x-ray inspection of both solid and wound golf balls has beenaccomplished using two methods. The first method is the golden imageprocess, which consists of taking an image of a “perfect” specimen (acontrol), placing it into memory, taking subsequent images of samples,and comparing them to the image of the “perfect” specimen. Thedifferences between the “perfect” image and the specimen are used todetermine the amount of error in the specimen.

The second method, typically for use on solid balls, includes the stepsof x-raying the specimen in such a manner that both the core and thecover are displayed. X-raying the ball in this manner allows directmeasurement of the thickness of the cover. This process generallyrequires the use of lower energy x-rays to so that the cover materialcan be seen clearly in the resulting image. Many times, the use of lowerpower causes the edges of the image to become distorted or less clear.The specimen can be doped to assist in cover detection.

Both methods may also include the step of doping the specimen so thatthe specimen is easier to x-ray. Doping a specimen, however, can haveadverse effects on the product. The golden image process is additionallysubject to error if the standard is at all less than perfect. Further,the positioning of the golf ball must be perfect. Any wobble in thefixture that holds the ball will affect the golden image test.

There are other limitations inherent in the micro focal x-ray machinesthat are utilized in industries such as the medical, integrated circuit,and printed circuit board industries. It should also be noted thatsimply using a micro focal x-ray is not sufficient to produce the sharpimages required for many imaging techniques. The device for convertingx-rays to visible light, called the image intensifier, must havesufficient resolution to produce a high quality image. Resolution isusually measured in line pairs per millimeter. For example, if an imageintensifier has a resolution of 4 line pairs per millimeter and anoptical gain of 2 it would be able to resolve an object ⅛ millimeter insize.

Because of these limitations and problems, there is, therefore, a needfor more suitable methods of determining the concentricity anddimensions of golf ball components using x-rays. Such a method ispresented by the present invention.

SUMMARY OF THE INVENTION

The present invention is directed to A method for inspecting a golf ballcomprising the steps of providing a golf ball comprising a core and acover; abutting the golf ball against at least one flat marker; rotatingthe golf ball about a single axis; capturing an x-ray image of the golfball and at least one marker; and determining the eccentricity of thegolf ball.

In one embodiment, the step of determining the eccentricity comprisesthe step of measuring the distance from the at least one marker to anouter surface of the core as the ball rotates about the single axis. Thedistance between the marker and the core surface are used to determinethe cover thickness. Ideally, the marker is opaque to x-rays, such aswith a metal marker. Preferably, the metal is aluminum, copper, steel,titanium, or a mixture thereof.

In another embodiment, there are at least two additional markersoriented to measure different axes. The x-ray has an intensity optimizedfor detecting the edge of the golf ball core. The core and the markerhave a first and second center and the distance between the two iscalculated at predetermined intervals to determine concentricity of thecore. Ideally, the x-ray has a spot size of less than about 0.035 inchesby 0.02 inches, preferably, less than about 0.01 inches by 0.01 inches,and most preferably, less than about 0.005 inches by 0.005 inches. It ispreferred that the x-ray has an intensity greater than the intensityrequired to detect the cover material such that the cover istransparent. Additionally, the cover opacity and the core opacity shouldbe different. In one preferred core construction, the core comprises acenter and an outer core layer. The x-ray intensity is preferablybetween about 25 and about 75 kV, more preferably between about 30 andabout 60 kV, and most preferably between about 35 and about 50 kV Thepresent invention is also directed to a method for inspecting a golfball comprising the steps of providing a golf ball comprising a core anda cover; restraining the golf ball between a flat surface and a rotatingconcave surface; rotating the golf ball about a single axis; providingat least two reference markers abutting the cover of the golf ball,wherein a first marker is embedded in and flush with the rotatingconcave surface and a second marker is on an axis perpendicular to theaxis of rotation; capturing an x-ray image of the golf ball; measuring afirst distance between the core center and the first marker and a seconddistance between the core center and the second marker; and determiningthe true eccentricity of the golf ball by combining the first and seconddistances using the following formula:$E_{True} = \sqrt{\left( {E_{1}^{2} + E_{2}^{2}} \right)}$where E₁ is the eccentricity along the axis of rotation and E₂ is theeccentricity perpendicular to the axis. The flat surface and rotatingconcave surface can be aligned along the axis of rotation.

A method for inspecting a golf ball comprising the steps of providing agolf ball comprising a core and a cover; restraining the golf ballagainst a rotating fixture; rotating the golf ball about a single axis;providing at least two reference markers abutting the cover of the golfball, wherein a first marker is embedded in the rotating fixture andabuts the cover, and a second marker is on an axis perpendicular to theaxis of rotation; capturing an x-ray image of the golf ball; measuring afirst distance between the core center and the first marker and a seconddistance between the core center and the second marker; and determiningthe true eccentricity of the golf ball by combining the first and seconddistances using the following formula:$E_{True} = \sqrt{\left( {E_{1}^{2} + E_{2}^{2}} \right)}$where E₁ is the eccentricity along the axis of rotation and E₂ is theeccentricity perpendicular to the axis. The golf ball may be restrainedagainst the rotating fixture with clamps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a golf ball shifted along an axis ofrotation;

FIG. 2 is a cross-sectional view of a golf ball and possibleeccentricity errors;

FIG. 3 is a depiction of x-ray focusing optics and the resulting spotsize and error;

FIG. 4 is a golf ball x-ray image according to the present invention;

FIG. 5 is an x-ray image at an intensity set to detect both cover andcore;

FIG. 6 is an x-ray image at an intensity set to detect only the core;and

FIG. 7 is an x-ray image depicting the markers and golf ball imagingsystem of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to the use of metal markers to inspectand better locate the surface and concentricity of a golf ball using anelectromagnetic energy source, such as x-rays. More particularly, theinvention is directed to the x-ray inspection of golf ballsincorporating markers opaque to x-ray imaging. The use of markers, andmetal markers in particular, makes it easier to particularly locate theouter surface of the golf ball for comparison with inner surfaces, suchas those defined by golf ball centers, cores, intermediate layers, andinner cover layers, when imaged with x-rays.

Metal markers are easily “seen” with x-ray imaging because of their lackof transmission of x-ray energy. X-rays are high-energy photons thathave higher energy and a shorter wavelength (typically about 0.3 nm toabout 2 nm), compared to the energy and wavelength (about 400 nm toabout 780 nm) of visible light. Anytime there is more matter between thex-ray source and the detection film, whether the matter is thicker orjust has a higher density, fewer x-rays are transmitted to the detectionfilm, which starts off whitish and darkens as various levels of x-raysstrike it. For example, bones appear lighter on a typical human x-rayimage because bone is denser than the rest of the body, and in dentalx-rays, metal fillings appear white, because the metal is very dense.

The marker(s) of the present invention are opaque to x-rays and,therefore, provide a very clear and defined edge and reference pointfrom which to measure core and layer dimensions against. Because theoptimal x-ray intensity for clearly discerning the core and its edges ismuch higher than the x-ray intensity that allows clear edge definitionof the cover, the metal markers allow the x-ray intensity to beoptimized for detecting the edge of the golf ball core without beingconcerned with seeing and using the cover as a reference point. Withoutthe markers, the x-ray intensity must be set at a compromising intensitywhere both cover and core can be seen (but with reduced contrast anddefinition). Referring to FIG. 5, the x-ray image of the golf ball wastaken at an intensity set to detect both the cover and the core. At thisintensity, the surface of the cover appears irregular and the surface ofthe core is out of focus. In FIG. 6, the x-ray intensity is set muchhigher, optimized for core detection. FIG. 6 clearly shows that, at thehigher x-ray intensity, the surface of the cover is undetectable withoutthe presence of the metal marker.

Preferably, one or more metal marker(s) are used, more preferablygreater than about two, and most preferably, at least about three. Themetal markers can be constructed of any material opaque to x-rays, butare preferably metal or blend of metals. More preferably, the markersare aluminum, steel, copper, or titanium. If more than one markers arepresent, they can be of the same or differing materials or metals.

In a preferred embodiment, the golf ball can be rotated and the centerof the ball calculated from the curved edge measurement. Then thedistance from the center to the metal marker can be calculated atpredetermined intervals to determine concentricity of the core.

In another preferred embodiment, the ball can be simultaneously measuredon multiple axes. This improves the measurement of concentricity bymaking it possible to detect whether the core is shifted, no matterwhich direction it is shifted.

Referring to FIGS. 1 and 2, when a ball is rotated about an axis tomeasure the eccentricity of its core, what is typically done is that thedistance from the surface to the core is measured repeatedly as itrotates. The difference between the maximum distance and the minimumdistance is measured and indicates how far off center the core is.However, the only eccentricity that is detected is that which isperpendicular to the axis of rotation. If the core happens to be shiftedalong the axis of rotation no eccentricity is detected at all. If thecore is shifted at some angle to the axis of rotation, the measuredeccentricity is less than the true eccentricity by the sine of theangle. According to the present invention, in order to find the trueeccentricity of the core, it is necessary to measure along the axis ofrotation as well as perpendicular to it.

Referring to FIG. 4, the x-ray image of a golf ball shows it beingrotated along its horizontal axis. In a preferred embodiment, the ballis rotated about an axis and the distance from the surface to the centerof the core is measure repeatedly. The intersecting lines indicatemeasurements from the center of the core to the metal markers. Thedifference between the maximum and minimum distance measure is taken todetermine how far off center the core is. The measurements are takenalong the axis of rotation as well as perpendicular to the axis. Thus,there are at least two measurements of eccentricity and they arepreferably combined using the Pythagorean theorem.$E_{True} = \sqrt{\left( {E_{1}^{2} + E_{2}^{2}} \right)}$The true eccentricity (E_(True)) is the square root of the eccentricityalong the axis of rotation (E₁), squared, plus the eccentricityperpendicular to the axis (E₂), squared.

Referring to FIG. 6, because of the nature of the preferred x-ray source(transmission type) and the lack of focusing lenses, the quality of theimage and the ability to resolve fine details is dependent on the sizeof the spot the radiation emanates from (the focal spot). Preferably,the x-ray source used has a small x-ray focal spot size. In general,x-ray spot size is around 0.035 inches by 0.02 inches. The resulting“band of unsharpness,” seen in FIG. 6, is about 0.017 inches to about0.010 inches. While this unsharpness is not a problem for imaging manytypes of golf balls, it can be a problem for golf balls having coverlayers of less than about 0.05 inches. In a preferred embodiment,therefore, the x-ray focal spot size in the present invention is lessthan about 0.01 inches by 0.01 inches. In a more preferred embodiment,the x-ray focal spot size is less than about 0.005 inches by 0.005inches. It is envisioned that a single lens or a combination of lensesmay be used to adjust the x-ray spot size to a desired area.

Referring to FIG. 7, preferably a golf ball is clamped between arotating cup A and a flat surface B. The cup A is made of a plasticmaterial, intended to be relatively transparent to x-rays. Inside thecup A, a metal marker C is held against the golf ball by a spring. Theflat surface B is also made of a plastic material with a 0.06-inchcovering of aluminum that serves as the metal marker C. A piece ofspring steel D that contacts the ball on its equator as it rotatesconstitutes another metal marker.

The image analysis is accomplished using an Insights® 2000 by Cognex, ofNatick, Mass. In a first method, the edge of the core and the edge ofthe marker are determined using the “find edge” tool and the distancebetween the core and the marker are measured at multiple locationsaround the ball to calculate eccentricity. In a preferred method thecore of the golf ball is located with a “find curve” tool. Each of themetal markers is located by finding their edges, the edge adjacent theball and the opposing edge, with a “find edge” tool. From this step, themiddle of the marker is determined by obtaining the difference betweenthe two edges. From this determination, the center of the golf ball coreto the center of each of the markers can be determined. In a mostpreferred method, the core of the golf ball is located with a “findcurve” tool. The center of each of the metal markers is located usingthe “find pattern” tool. The “find curve” and “find pattern” tools gavethe most accurate and repeatable measurements.

The center of the core and center of the markers are determined becausechanges to the x-ray intensity can alter the apparent size of an object,but do not effect the actual location. As the x-ray intensity isincreased, for example, the core may appear to decrease in diameterwhile the center remains in the same location. It is believed that thiseffect results from the large focal spot size of the x-ray source(roughly 0.9 mm×0.5 mm), as described above in depicted in FIG. 3.

Below is a table that compares the results of x-ray and another commonmethod of obtaining golf ball dimensions, ultrasonic measurements. Theultrasonic measurements are of a urethane outer cover and mantle layermeasured at 90° intervals all around the ball. The eccentricity wascalculated using the square root of the sum of the squares, as describedabove. The identical golf balls were x-ray inspected a variety of timesusing the method of the invention. X-ray eccentricity is expressed as arange from the highest to the lowest value obtained.

TABLE 1 Ultrasonic Measurements X-ray Ball # Bottom Left Right FrontBack Top Eccentricity Eccentricity Good #4 38 34 40 39 36 38 3.35 U.S.C.§  2.1-10.5 Good #2 41 40 41 42 39 34 3.84 3.0-7.3 Good #9 38 39 36 4236 34 3.91  3.8-11.5 Good #6 35 35 34 36 34 40 2.74 2.8-7.9 Good #12 3432 35 35 33 40 3.50 4.6-8.4 Bad #6 37 38 36 35 36 23 7.09 13.8-18.5 Bad#4 36 43 37 37 37 24 6.71   15-20.7 Bad #5 36 37 37 34 34 26 5.0012.6-17.3 Bad #12 36 36 37 36 38 25 5.61 11.8-17  

The term “about,” as used herein in connection with one or more numbersor numerical ranges, should be understood to refer to all such numbers,including all numbers in a range.

The invention described and claimed herein is not to be limited in scopeby the specific embodiments herein disclosed, since these embodimentsare intended solely as illustrations of several aspects of theinvention. Any equivalent embodiments are intended to be within thescope of this invention. Indeed, various modifications of the inventionin addition to those shown and described herein will become apparent tothose skilled in the art from the foregoing description. Suchmodifications are also intended to fall within the scope of the appendedclaims.

1. A method for inspecting a golf ball comprising the steps of:providing a golf ball comprising a core having a first diameter and atleast one cover layer having a first thickness; securing said golf ballin a measuring holder; providing an x-ray source having a spot size andan intensity optimized for detecting the edge of the golf ball core orcover layer, the first diameter, or the first thickness, the x-rayintensity being between about 25 keV and about 75 keV; reducing thex-ray spot size to less than about 0.01 inches by 0.01 in resulting bandof unsharpness is no greater than about 0.010 inches; providing at leastone marker placed within the measuring holder; abutting the golf ballagainst said at least one marker; rotating the golf ball about at leastone axis; capturing an x-ray image of the golf ball about at least oneaxis and an image of the marker; and determining the eccentricity of thegolf ball.
 2. The method of claim 1, wherein the x-ray intensity isbetween about 30 keV and about 60 keV.
 3. The method of claim 2, whereinthe x-ray intensity is between about 35 keV and about 50 keV.
 4. Themethod of claim 1, wherein the x-ray has a spot size of less than about0.005 inches by 0.005 inches.
 5. The method of claim 1, wherein the corecomprises a center and an outer core layer.
 6. The method of claim 1,wherein the step of determining the eccentricity comprises the step ofmeasuring the distance from the at least one marker to an outer surfaceof the core as the ball rotates about the single axis.
 7. The method ofclaim 1, wherein the distance between the marker and the care surfaceare used to determine the cover thickness.
 8. The method of claim 1,wherein the marker is opaque to x-rays.
 9. The method of claim 1,wherein the marker is metal.
 10. The method of claim 9, wherein themetal is aluminum, copper, steel, titanium, or a mixture thereof. 11.The method of claim 1, further comprising at least two markers orientedto measure different axes.
 12. The method of claim 1, wherein the coreand the marker have a first and second center and the distance betweenthe two is calculated at predetermined intervals to determineconcentricity of the core.
 13. The method of claim 1, wherein the x-rayintensity is a first intensity greater than a second intensity requiredto detect the cover material, the first and second intensities beingdifferent in an amount such that the cover is transparent at the firstintensity.
 14. The method of claim 1, wherein the cover has a firstopacity and the core has a second opacity different from the first.